1. Field of the Invention
The present invention relates to a driving device and a light amount controller using the driving device.
2. Description of the Related Art
Conventionally, a driving device which is reduced in diameter around the center of a rotation axis and at the same time increased in output has been proposed in Japanese Laid-Open Patent Publication (Kokai) No. 2002-49076.
FIG. 10 is an exploded perspective view of the driving device disclosed in the above-mentioned publication, and FIG. 11 is an axial cross-sectional view of the driving device shown in FIG. 1.
In these figures, reference numeral 1001 designates a magnet, 1002 a coil, 1003 a stator, 1004 an auxiliary stator, and 1005 a base plate.
The magnet 1001 is comprised of a bottomed hollow cylindrical magnet body 1001a, a drive pin 1001b formed integrally with the magnet body 1001a in a manner axially protruding from a portion of a peripheral wall of the magnet body 1001a, and shaft parts 1001c and 1001d axially protruding from the opposite sides of the center of the bottom wall of the magnet body 1001a. In the magnet 1001, the peripheral wall of the magnet body 1001a is circumferentially divided into four sections which are magnetized such that they have alternately different S and N poles.
The coil 1002 is formed by winding wire around an annular groove of a cylindrical bobbin. The coil 1002 is disposed within the stator 1003 in a manner extending along the axis of the magnet 1001.
The stator 1003 has a bottomed hollow cylindrical body, which has an outer peripheral wall thereof formed with a protruding piece-like outer magnetic pole part 1003a extending along the axis of the hollow cylindrical body, and a shaft-like protrusion 1003b extending along the axis of the hollow cylindrical body from the center of the inner bottom wall of the hollow cylindrical body. The shaft-like protrusion 1003b has a front end thereof formed therein with a shaft hole 1003c, in which the shaft part 1001c is rotatably fitted. Further, the coil 1002 is rigidly fitted on a base end portion of the shaft-like protrusion 1003b. The stator 1003 is magnetized by the coil 1002.
The auxiliary stator 1004 has a hollow cylindrical shape, and is rigidly fitted on the front end of the shaft-like protrusion 1003b of the stator 1003 in opposed relation to the coil 1002. The auxiliary stator 1004 and the shaft-like protrusion 1003b cooperate to form an inner magnetic pole part.
The base plate 1005 has a circular opening 1005a formed in the center thereof, an arcuate guide slot 1005b formed therein radially outward of the circular opening 1005a, and a shaft hole 1005c formed therein in the vicinity of the arcuate guide slot 1005b. The drive pin 1001b of the magnet 1001 is slidably engaged in the guide slot 1005b of the base plate 1005. Further, the shaft part 1001d of the magnet 1001 is rotatably fitted in the shaft hole 1005c of the base plate 1005.
The outer magnetic pole part 1003a of the stator 1003 is opposed to the outer peripheral surface of the magnet body 1001a with a clearance therebetween, and the outer peripheral surface of the inner magnetic pole part formed by the auxiliary stator 1004 and the shaft-like protrusion 1003b of the stator 1003 is opposed to the inner peripheral surface of the magnet body 1001a with a clearance therebetween.
In the driving device constructed as above, the magnet 1001 is angularly reciprocated about the shaft parts 1001c and 1001d within a limited range by switching the direction of energization of the coil 1002 and thereby changing the polarity of the outer magnetic pole part 1003a and that of the inner magnetic pole part (the protruding part 1003b and the auxiliary stator 1004).
The angular reciprocation of the magnet 1001 is restricted by the guide hole 1005b formed in the base plate 1005 and the drive pin 1001b engaged in the guide hole 1005b. 
In the driving device configured as above, magnetic flux generated by energization of the coil 1002 flows from the outer magnetic pole part 1003a to the opposed inner magnetic pole part, or from the inner magnetic pole part to the outer magnetic pole part 1003a opposed thereto, to effectively act on the magnet 1001 located between the outer magnetic pole part 1003a and the inner magnetic pole part.
The distance between the outer magnetic pole part 1003a and the inner magnetic pole part is set to a value obtained by adding together the thickness of the hollow cylindrical magnet body 1001a, the clearance between the magnet body 1001a and the outer magnetic pole part 1003a, and the clearance between the magnet body 1001a and the inner magnetic pole part, i.e. to a minimum possible value, which makes it possible to reduce the resistance of a magnetic circuit formed by the outer magnetic pole part 1003a and the inner magnetic pole part. As the resistance of the magnetic circuit is smaller, a larger amount of magnetic flux can be generated by a small electric current, leading to an increase in the output of the driving device.
In the above driving device disclosed in Japanese Laid-Open Patent Publication (Kokai) No. 2002-49076, the resistance of the magnetic circuit is reduced by setting the distance between the outer magnetic pole part 1003a and the inner magnetic pole part to the minimum possible value as stated above.
However, in the driving device configured as above, the predetermined clearances are provided, respectively, between the magnet body 1001a and the outer magnetic pole part 1003a and between the magnet body 1001a and the inner magnetic pole part, and hence there is room for improvement in terms of reduction of the resistance of the magnet circuit. For example, if one of the clearances can be dispensed with, the distance between the outer magnetic pole part 1003a and the inner magnetic pole part can be shortened, and therefore reduction of the resistance of the magnet circuit can be expected.
Further, in the driving device in which the predetermined clearance is provided between the magnet body 1001a and the opposed inner magnetic pole part, as stated above, it is necessary to control the clearance in course of manufacture, and hence the driving device still remains to be improved in terms of cost reduction as well. If the above-mentioned clearance can be omitted, the clearance control becomes unnecessary, which contributes to reduction of the costs.
Furthermore, according to a light amount controller disclosed in Japanese Laid-Open Patent Publication (Kokai) No. 2002-49076 referred to above, when it is desired to carry out a plurality of driving operations for driving shutter blades, aperture blades, and the like, it is necessary to provide a number of driving devices corresponding to the number of the driving operations needed on the base plate 1005. For example, most of the existing compact digital cameras have a plurality of driving devices provided on the base plate 1005, and hence the base plate 1005 is almost covered with the driving devices.